Currently, FDD (Frequency-division duplexing) of UMTS (Universal Mobile Telecommunications System) supports only one nominal bandwidth (also referred to as nominal channel spacing) and one chip rate. That is, a nominal bandwidth of 5 Mega Hertz (referred to as MHz for short) corresponds to a chip rate of 3.84 Mega chips per second (referred to as Mcps for short). Future service demands have higher requirements on the UMTS, including wider coverage, higher capacity and rate, and larger number of supported connection, such as MTC (Machine type communication) service. To support a higher rate, a potential technical solution is to make the UMTS support less bandwidth (less than 5 MHz) and employ narrow band carrier aggregation. With this technology, the link performance and system capacity of the UMTS can be effectively improved. In addition, with the gradually exiting of the global system for mobile communications (Global System For Mobile Communications, referred to as GSM for short), a realistic question is how to reform the spectrum of the GSM. The less bandwidth and the narrow band carrier aggregation technique provide the probability of aggregating the spectrum of the GSM for the UMTS system.
In the discussion of the standard of the NCT (New Carrier Type) in LTE (Long Term Evolution), a standalone NCT manner and a non-standalone NCT manner are proposed. As with legacy carrier, in the standalone NCT, a synchronous/broadcast/common channel is supported, to provide the terminal with access reference. The non-standalone carrier is mainly adapted to provide data transmission. The synchronous/broadcast/common channel can be selectively deleted for reducing the system overhead, and thus the non-standalone does not support access of a user.
In the conventional art, the less bandwidth is realized by reducing the chip rate, in which the original frame structure is remained unchanged, i.e., the number of the sampling points of the chip contained in the frame is unchanged, which is equivalent to lengthening the physical time of the frame. However, the system performance with this method is not good enough. For example, the delay is relatively longer. Further, in the case that a terminal supports carrier aggregations with different bandwidths, the complexity of the terminal is increased greatly. Another way to make the UMTS support less bandwidth is to redesign the frame structure, which needs to redefine the carrier bandwidth to be supported and the corresponding chip rate. In the conventional art, one way is to divide the bandwidth of 5 MHz uniformly. For example, the bandwidth of 5 MHz is divided into 2, 3 or 4 segments uniformly, following three system bandwidths are supported: 2.5 MHz, 1.66 MHz and 1.25 MHz, and the corresponding chip rates are respectively 1.92 Mcps, 1.28 Mcps and 0.96 Mcps.
Referring to FIG. 1, the bandwidth of 5 MHz is divided into 4 segments uniformly. Assuming that only one standalone small carrier is provided in the legacy bandwidth of 5 MHz, C2 is a standalone carrier, and C0, C1 and C3 are non-standalone carriers. If a narrow bandwidth is formed by dividing the legacy bandwidth of 5 MHz uniformly, and in the case that the legacy bandwidth of 5 MHz is divided into N (assuming that N<=5, i.e., the lest bandwidth is 1 MHz) narrow band carriers uniformly, the lest spacing Δfmin between the center of the narrow band carrier and the center frequency of the original bandwidth of 5 MHz is:
      Δ    ⁢                  ⁢          f      min        =      {                            0                                      N            =            3.5                                                            1.25            ⁢                                                  ⁢            MHz                                                N            =            2                                                            0.625            ⁢                                                  ⁢            MHz                                                N            =            4                              
In the conventional UMTS system, the channel raster Δf is 0.2 MHz. It can be seen from above equation that in the case that N is an even number, it cannot be ensured that the distance between the narrow band carrier and the center frequency of the legacy carrier is integral multiples of 0.2 MHz, no matter which narrow band carrier is set as the standalone carrier. However, in the case that N is an odd number, the standalone narrow band is provided at the center frequency of the legacy bandwidth of 5 MHz, i.e., it can be ensured that the standalone narrow band is swept at a frequency sweep granularity of 0.2 MHz. With this method, only in the case that the N is an odd number, it can be ensured that the narrow band carrier is swept at the frequency sweep granularity of 0.2 MHz. If a new frequency sweep granularity and a frequency sweep initial offset are introduced, the frequency sweep time of the terminal is increased greatly. Thus, with the way of dividing the bandwidth of 5 MHz uniformly, the frequency sweep time of the terminal is increased, and the number of the less bandwidth that can be supported is restrained.